1. Field of Invention
This invention relates to a rare earth titanate-based dielectric composition, and more particularly to a rare earth titanate-based dielectric composition that can be used to form multilayer ceramic chip capacitors having internal base metal electrodes formed of copper or copper alloys.
2. Background of the Invention
Multilayer ceramic chip capacitors have been widely utilized as miniature-sized, high capacitance, and high reliability electronic components. In accordance with increasing demands for high-performance electronic equipment, multilayer ceramic chip capacitors also have encountered marketplace demand for smaller size, higher capacitance, lower cost, and higher reliability.
Multilayer ceramic chip capacitors generally are fabricated by forming alternating layers of an internal electrode forming paste and a dielectric layer-forming paste. Such layers are typically formed by sheeting, printing, or similar techniques, followed by concurrent firing.
Generally, the internal electrodes have been formed of conductors such as palladium, gold, silver or alloys of the foregoing. Although palladium, gold and silver are expensive, they can be partially replaced by the use of relatively inexpensive base metals such as copper and its alloys. A “base metal” is a conductive metal other than gold, silver, palladium, and platinum. Base metal internal electrodes can become oxidized if fired in ambient air, so the dielectric layers and internal electrode layers must be co-fired in a reducing atmosphere. Firing in a reducing atmosphere, however, causes the dielectric layers to be reduced, which decreases resistivity. Multilayer ceramic chip capacitors using non-reducible dielectric materials have been proposed, however, such devices typically have a shorter life of insulation resistance (IR) and low reliability.
The Electronic Industry Association (EIA) prescribes a standard for the temperature coefficient of capacitance (TCC) known as the COG characteristic. The COG characteristic requires that the change of capacitance be no greater than 30 ppm per degree centigrade (30 ppm/° C.) when C>20 pF and within the limit of +120 ppm/° C. and −40 ppm/° C. when C≦20 pF over the temperature range −55° C. to +125° C. COG components do not exhibit any capacitance aging.